Recently, there has been considerable interest within the detergent industry for detergents which are "compact" and therefore, have lower dosage volumes. As a result, many attempts have been made to produce higher bulk density detergents. Compact detergents are currently in high demand as they conserve resources and are more convenient for consumers.
Generally, there have been two primary types of processes by which detergent particles or powders can be prepared. The first type of process involves spray-drying an aqueous detergent slurry in a spray-drying tower to produce highly porous detergent particles. In the second type of process, the various detergent ingredients are mixed after which they are agglomerated with an agglomeration agent or binder. In both processes, the most important factors which govern the density of the resulting detergent granules are the density, porosity, particle size and surface area of the various starting ingredients. These parameters, however, can only be varied within a limited range and through an agglomeration process alone density typically ranges from 700-750 g/l (Porasik, U.S. Pat. No. 4,427,417). Thus, these processes have been unable to consistently deliver a detergent bulk density higher than 900 g/l with an acceptable particle size distribution so as not to cause problems with product flowing or clumping.
There have been many attempts in the art for increasing the bulk density of detergent particles or powders. Particular attention has been given to densification of spray-dried particles by "post-tower" treatments. For example, one attempt involves a batch process in which spray-dried or granulated detergent powders containing sodium tripolyphosphate and sodium sulfate are densified and spheronized in a Marumerizer.RTM.. This apparatus comprises a substantially horizontal, roughened, rotatable table positioned within and at the base of a substantially vertical, smooth walled cylinder. This process, however, is essentially a batch process and is therefore less suitable for the large scale production of detergent powders. More recently, other attempts have been made to provide a continuous process for increasing the density of "post-tower" or spray dried detergent particles. Typically, such processes require a first apparatus which pulverizes or grinds the particles and a second apparatus which increases the density of the pulverized particles by agglomeration. These processes achieve the desired increase in density only by treating or densifying "post-tower" or spray-dried particles.
However, all of the aforementioned processes are directed primarily for densifying or otherwise processing spray dried particles. Currently, the relative amounts and types of ingredients which can be subjected to spray-drying is limited. In addition, the relative capital cost for spray drying equipment and energy consumption are prohibitive for high volume detergent products.
To that end, many attempts have been made to discover satisfactory agglomeration techniques for producing granular detergent products. However, the processes to date have been unable to produce agglomerated high density detergent products which have a density of at least about 900 g/l which also display acceptable particle size ranges. For acceptable consumer detergent products high levels of undersized particles ("fines") create dust during pouring, create free flowing or clumping problems, and display undesirable product appearance. Current agglomeration processes that produce detergent products with a high bulk density generate inordinate amounts of undersized particles ("fines"), and thus, fail to provide acceptable particle size distributions so as not to cause problems with product flowing or clumping.
Accordingly, there remains a need in the art for a process which produces a high density detergent composition having superior flow and particle size properties. Also, there remains a need for such a process which is more efficient and economical to facilitate large-scale production of high density detergent products.